5. SS7 Protocol Stack

SS7 is a layered signaling suite:

• MTP Levels 1–3: physical data link, reliable link transfer, routing + network management
• SCCP: extended addressing and routing (e.g., global titles), plus service classes
• TCAP: transaction and dialogue mechanisms for service queries
• Application Parts: service-specific protocols (ISUP, MAP, CAP, INAP, etc.)

TCAP is part of OSI layer 7 in the SS7 architecture view (Q.771).

5.1 Message Transfer Part (MTP)

MTP Level 1 — Signaling data link (physical)